1. Field of the Invention
This invention relates to apparatuses for capping containers such as bottles, and in particular to rotary type capping apparatuses for screwing caps, such as screw caps and PP ( pilferproof ) caps, onto the mouth of containers for tight sealing thereof.
2. Description of the Prior Art
Various capping apparatuses have been used for automatically capping bottles after having them filled with desired contents. One category of such capping apparatuses includes rotary type capping apparatuses in which caps are screwed onto the mouth, which is usually threaded, of containers to be capped. Typical examples of caps to be used in this category of capping apparatuses include screw caps and the so-called PP (pilferproof) caps which may be removably and tightly held onto the mouth of containers when screwed. Thus, in typical prior art rotary type capping apparatuses, containers transported from a previous station as filled with desired contents are temporarily held in position, and then capping heads having caps to be applied to the containers are lowered thereby having the caps screwed onto the mouths of the containers.
Typically, the prior art rotary type capping apparatuses include a rotary turn table having a plurality of container holders disposed along the periphery of the table and a plurality of capping heads which are each provided corresponding in position to the container holders and driven to move along a circular path together with the turn table. Each of the capping heads has a cap holder which releasably holds a cap at its bottom and which is driven to rotate so as to have the cap screwed onto the mouth of the container held by the corresponding container holder on the turn table. In such prior art rotary type capping apparatuses, a fixed sun gear is commonly provided coaxially with a rotary shaft of the turn table and a plurality of pinions are provided in mesh with and disposed around the sun gear. Each of the pinions is fixedly provided on a driving shaft which is operatively connected to the corresponding cap holder so that the cap holder may be driven to rotate when the corresponding pinion moves around the sun gear in mesh therewith, thereby causing the cap held by the cap holder to be screwed onto the mouth of the corresponding container.
However, in such prior art rotary type capping apparatuses, since the rotation of each pinion around its own axis depends upon the rotation of the turn table, a torque for screwing a cap onto a container is directly determined by the rotation of the turn table. As a result, if the rotation of the turn table varies, the screwing torque also varies accordingly. This has been found to be extremely disadvantageous because the rotational speed of the turn table is sometimes desired to be set at different levels in connection with other processing stations in the same container handling line, such as a filling station where desired contents are filled in containers and a labelling station where labels are glued to containers. Moreover, when the turn table is accidentally halted for some reason, an operator cannon be sure as to which of the containers then held on the turn table are properly capped, and, thus, all of the containers must be inspected one by one before resuming the capping operation. Still further, since the screwing torque is a function of the rotational speed of the turn table, as set forth above, the degree of cap tightening tends to fluctuate thereby requiring a careful inspection after capping, or, alternatively, provision of an expensive speed control mechanism for maintaining the rotational speed at a desired value at all times.